Analysis of working principle of solid state relay

Compared with electromechanical relay, solid state relay (SSR) is a relay without mechanical movement and no moving parts, but it has essentially the same function as electromechanical relay. SSR is a non-contact switching element composed entirely of solid-state electronic components. It uses the point, magnetic and optical characteristics of electronic components to complete the reliable isolation of input and output. It uses high-power transistors, power FETs, and single-term controllable. The switching characteristics of devices such as silicon and triacs can achieve contactless and spark-free connection and disconnection of the controlled circuit.

The working principle of solid state relay

Solid State Relay (Solid State Relay SSR) is a new type of non-contact electronic switching device developed by the combination of modern microelectronic technology and power electronic technology. It can realize the use of weak control signals (a few milliamperes to tens of milliamperes) to control a current load of 0.1A up to several hundred A, and conduct contactless connection or disconnection. The solid state relay is a four-terminal device with two input terminals and two output terminals. The input terminal is connected to the control signal, and the output terminal is connected in series with the load and power supply. The SSR is actually a controlled power electronic switch

Solid state relays are different from ordinary electromagnetic relays: no contact, optical (electrical) isolation between the input circuit and the output circuit, and discrete components. Semiconductor microelectronic circuit chips and power electronic devices are assembled, using flame-retardant epoxy resin as raw material, and using potting technology to keep it enclosed in the shell to isolate it from the outside world. It has good pressure resistance, anti-corrosion, moisture-proof and anti-vibration performance. The solid state relay is composed of three parts: input circuit, drive circuit and output circuit. Here only take the AC zero-crossing solid state relay which is widely used as an example to introduce its working principle. The circuit uses zero-crossing trigger technology, which has the characteristics of turning on when the voltage crosses zero and turning off when the negative current crosses zero. A complete sinusoidal waveform can be obtained on the load, so the radio frequency interference of the circuit is very small.